The present invention is directed toward methods and apparatuses for controlling the intensity of a radiation beam directed toward a microlithographic substrate. Microelectronic features are typically formed in microelectronic substrates (such as semiconductor wafers) by selectively removing material from the wafer and filling in the resulting openings with insulative, semiconductive, or conductive materials. One typical process includes depositing a layer of radiation-sensitive photoresist material on the wafer, then positioning a patterned mask or reticle over the photoresist layer, and then exposing the masked photoresist layer to a selected radiation. The wafer is then exposed to a developer, such as an aqueous base or a solvent. In one case, the photoresist layer is initially generally soluble in the developer, and the portions of the photoresist layer exposed to the radiation through patterned openings in the mask change from being generally soluble to become generally resistant to the developer (e.g., so as to have low solubility). Alternatively, the photoresist layer can be initially generally insoluble in the developer, and the portions of the photoresist layer exposed to the radiation through the openings in the mask become more soluble. In either case, the portions of the photoresist layer that are resistant to the developer remain on the wafer, and the rest of the photoresist layer is removed by the developer to expose the wafer material below.
The wafer is then subjected to etching or metal disposition processes. In an etching process, the etchant removes exposed material, but not material protected beneath the remaining portions of the photoresist layer. Accordingly, the etchant creates a pattern of openings (such as grooves, channels, or holes) in the wafer material or in materials deposited on the wafer. These openings can be filled with insulative, conductive, or semiconductive materials to build layers of microelectronic features on the wafer. The wafer is then singulated to form individual chips, which can be incorporated into a wide variety of electronic products, such as computers and other consumer or industrial electronic devices.
As the size of the microelectronic features formed in the wafer decreases (for example, to reduce the size of the chips placed in electronic devices), the size of the features formed in the photoresist layer must also decrease. In some processes, the dimensions (referred to as critical dimensions) of selected features are evaluated as a diagnostic measure to determine whether the dimensions of other features comply with manufacturing specifications. Critical dimensions are accordingly selected to be the most likely to suffer from errors resulting from any of a number of aspects of the foregoing process. Such errors can include errors generated by the radiation source and/or the optics between the radiation source and the mask. The errors can also be generated by the mask, by differences between masks, and/or by errors in the etch process. The critical dimensions can also be affected by errors in processes occurring prior to or during the exposure/development process, and/or subsequent to the etching process, such as variations in deposition processes, and/or variations in material removal processes, such as chemical-mechanical planarization processes.
One general approach to correcting lens aberrations in wafer optic systems (disclosed in U.S. Pat. No. 5,142,132 to McDonald et al.) is to reflect the incident radiation from a deformable mirror, which can be adjusted to correct for the aberrations in the lens optics. However, correcting lens aberrations will not generally be adequate to address the additional factors (described above) that can adversely affect critical dimensions. Accordingly, another approach to addressing some of the foregoing variations and errors is to interpose a gradient filter between the radiation source and the mask to spatially adjust the intensity of the radiation striking the wafer. Alternatively, a thin film or pellicle can be disposed over the mask to alter the intensity of light transmitted through the mask. In either case, the filter and/or the pellicle can account for variations between masks by decreasing the radiation intensity incident on one portion of the mask relative to the radiation intensity incident on another.
One drawback with the foregoing arrangement is that it may be difficult and/or time-consuming to change the gradient filter and/or the pellicle when the mask is changed. A further drawback is that the gradient filter and the pellicle cannot account for new errors and/or changes in the errors introduced into the system as the system ages or otherwise changes.
The present invention is directed to methods and apparatuses for controlling the intensity distribution of radiation directed to microlithographic substrates. In one aspect of the invention, the method can include directing a radiation beam from a radiation source along radiation path, with the radiation beam having a first distribution of intensity as a function of location in a plane generally transverse to the radiation path. The method can further include impinging the radiation beam on an adaptive structure positioned in the radiation path, and changing an intensity distribution of the radiation beam from the first distribution to a second distribution different than the first distribution by changing a state of a first portion of the adaptive structure relative to a second portion of the adaptive structure. The method can further include directing the radiation beam away from the adaptive structure along the radiation path and impinging the radiation beam directed away from the adaptive structure on the microlithographic substrate.
In a further aspect of the invention, the method can include impinging a first portion of the radiation beam on a first portion of a reflective medium and impinging a second portion of the radiation beam on a second portion of the reflective medium. The method can further include moving the first portion of the reflective medium relative to the second portion, and reflecting at least part of the first portion of the radiation beam toward a first portion of a grating having a first transmissivity, and reflecting at least part of the second portion of the radiation beam toward a second portion of the grating having a second transmissivity greater than the first transmissivity. At least part of the second portion of the radiation beam then passes through the grating to impinge on the microlithographic substrate, while at least part of the first portion of the radiation beam is attenuated or blocked from passing through the grating.
The invention is also directed toward an apparatus for controlling an intensity distribution of radiation directed to a microlithographic substrate. The apparatus can include a substrate support having a support surface positioned to carry a microlithographic substrate, and a source of radiation positioned to direct a radiation beam along a radiation path toward the substrate support. The apparatus can further include an adaptive structure positioned in the radiation path and configured to receive the radiation beam with a first intensity distribution and transmit the radiation beam with a second intensity distribution different than the first intensity distribution. The adaptive structure can have a first portion and a second portion, each positioned to receive the radiation and changeable from a first state to a second state, wherein the adaptive structure is configured to transmit the radiation with the second intensity distribution when the first portion is in the first state and the second portion is in the second state. The apparatus can further include a controller operatively coupled to the adaptive structure to direct at least one of the first and second portions to change from the first state to the second state to change an intensity distribution of the radiation beam from the first intensity distribution to the second intensity distribution.
In a further aspect of the invention, the adaptive structure can include a selectively transmissive medium having a first portion aligned with a first portion of the radiation beam when the radiation beam is emitted from the radiation source, and a second portion aligned with the second portion of the radiation beam. Each of the first and second portions can have a transmissivity that is changeable from a first transmissivity to a second transmissivity different than the first transmissivity. Alternatively, the adaptive structure can include a reflective medium having a first portion aligned with a first portion of the radiation beam when the radiation beam is emitted from the radiation source, and a second portion aligned with a second portion of the radiation beam. Each of the first and second portions of the reflective medium can be coupled to at least one actuator to move from a first inclination angle relative to the radiation path to a second inclination angle relative to the radiation path, with the second inclination angle being different than the first inclination angle.